1 | use std::future::Future; |
2 | use std::pin::Pin; |
3 | use std::task::{Context, Poll}; |
4 | |
5 | /// Converts a function to a future that completes on poll. |
6 | pub(crate) struct BlockingTask<T> { |
7 | func: Option<T>, |
8 | } |
9 | |
10 | impl<T> BlockingTask<T> { |
11 | /// Initializes a new blocking task from the given function. |
12 | pub(crate) fn new(func: T) -> BlockingTask<T> { |
13 | BlockingTask { func: Some(func) } |
14 | } |
15 | } |
16 | |
17 | // The closure `F` is never pinned |
18 | impl<T> Unpin for BlockingTask<T> {} |
19 | |
20 | impl<T, R> Future for BlockingTask<T> |
21 | where |
22 | T: FnOnce() -> R + Send + 'static, |
23 | R: Send + 'static, |
24 | { |
25 | type Output = R; |
26 | |
27 | fn poll(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<R> { |
28 | let me = &mut *self; |
29 | let func = me |
30 | .func |
31 | .take() |
32 | .expect("[internal exception] blocking task ran twice." ); |
33 | |
34 | // This is a little subtle: |
35 | // For convenience, we'd like _every_ call tokio ever makes to Task::poll() to be budgeted |
36 | // using coop. However, the way things are currently modeled, even running a blocking task |
37 | // currently goes through Task::poll(), and so is subject to budgeting. That isn't really |
38 | // what we want; a blocking task may itself want to run tasks (it might be a Worker!), so |
39 | // we want it to start without any budgeting. |
40 | crate::runtime::coop::stop(); |
41 | |
42 | Poll::Ready(func()) |
43 | } |
44 | } |
45 | |